In the development of weapon systems, strength, weight and size are prime considerations. As materials and production techniques have improved, proportionate reductions in weapon weight and size are achieved at the expense of no significant increase in component strength. A certain degree of weapon stoppages have been endured due to parts breakage, often at very critical times, resulting in losses of life and combat effectiveness.
Continued use of a weapon has a degrading effect upon the reliability, availability, and maintainability of its mechanical system. Weapon part life, in general, is not time related but use related. Reliability can be significantly improved when certain components are replaced on a planned schedule prior to predicted failure or wearout. Significant data ordinarily exists as a result of extensive development testing concerning the wearout characteristics of a component and its expected life. Additional data may be attained when required through variability analysis and probabilistic design techniques. For planned replacement of parts to be effective, however, there must be a means to measure the wear or condition of the weapon system.